class Solution(object):
    def reverseString(self, s):
        """
        :type s: List[str]
        :rtype: None Do not return anything, modify s in-place instead.
        """
        mid = len(s) // 2
        for i in range(mid):
            change_char = s[i]
            s[i] = s[len(s) - 1 - i]
            s[len(s) - 1 - i] = change_char
